The selection of social actions in families: II. Parental investment

One of the most widely used applications of kin selection concerns the inve stment that parents provide to their young. In particular, Trivers' concept of parent-offspring conflict was enthusiastically adopted by biologists an d applied to many aspects of parent-offspring interactions, including repro ductive effort, clutch size, brood reduction, sex ratios, and dispersal and germination strategies In this paper, parental and offspring strategies ar e examined with regard to the amount of resources that parents invest in ea ch offspring; this determines the size and average fitness of the newly ind ependent young. Parental investment is used here as a model system to compa re the results of genetic models of social actions with those of autonomous gene models, and to examine the relative merits of using measures of inclu sive or collective fitness. To this end, the extent of conflicts over paren tal investment is derived for two kinds of families, which differ in the wa y that the young compete with each other (equal versus unequal competition) . Finally, the ways in which conflicts are resolved and the relative import ance of conflict and cooperation in raising young are discussed.